# Unproven claim in Weinberg's textbook

dEdt
In his Lectures on Quantum Mechanics, Weinberg makes the following claim about solutions to the Schrodinger equation for a central potential: Suppose $\psi(\mathbf{x},t)$ is an eigenfunction of $H$, $\mathbf{L}^2$, and $L_z$. According to Weinberg, "since $\mathbf{L}^2$ acts only on angles, such a wavefunction must be proportional to a function only of angles, with a coefficient of proportionality $R$ that can depend only on $r$. That is, for all r,
$$\psi(\mathbf{x})=R(r)Y(\theta,\phi)."$$

He does not elaborate further on this, in my view, non-trivial statement. Can someone here provide a proof of his claim?

Mentor
He does not elaborate further on this, in my view, non-trivial statement. Can someone here provide a proof of his claim?

I'd be inclined to work on the intuition behind that claim instead of looking for a rigorous proof, because the general idea is useful in so many other problems.

But first, which part of the statement are you asking about? The part about ##L^2## acting only on ##\theta## and ##\phi##, or the claim that this implies the ##R(r)Y(\theta,\phi)## form of the solution?

dEdt
I'm talking about the claim that $\psi=R(r)Y(\theta,\phi)$ given that $\mathbf{L}^2$ acts only on angles.